Exam 2 Study Guide

Winds

• Dust storms are influenced by fine-grained soils, lack of vegetation, and high winds.
• Winds impact:
  • Weather patterns.
  • Natural hazards.
  • Energy generation.
  • Transportation.
  • Aesthetics of landscapes.

Atmospheric Forces and Global Wind Patterns

• Winds are generated by atmospheric forces:
  • Gravity
  • Pressure gradient
  • Coriolis effect
  • Friction

Gravity:

• Pulls air downward, creating pressure differences.
• Higher pressure closer to earth’s surface
• Pressure decreases rapidly with increased altitude
• Small elevation changes result in significant change in air pressure

Pressure Gradient Force:

• Moves air from high to low pressure, causing winds. Air moves horizontally from areas of high pressure to areas of low pressure: air movement = wind
  • Low Pressure: warm air rises (less dense); creates lower surface pressure; air converges from high-pressure areas
  • High Pressure: cool, dry air descends (more dense); creates higher surface pressure; air diverges to low-pressure areas

Coriolis Effect:

• Rotation of the earth “deflects” path of moving air: Moving air bends right in northern hemisphere, left in southern hemisphere.

Friction:

• Surfaces / surface roughness can slow winds. Friction with objects at the surface can move these objects (e.g. leaves, dust).

Isobaric maps:

• Isobaric maps show the distribution of pressure (lines of equal pressure, called isobars).
• Pressure gradient: difference in pressure between areas, strongest when isobars are close together (large gradient), and weaker when they are farther apart (small gradient).
  • Pressure changes, and therefore the pressure gradient, are greatest perpendicular to the isobars.

Weather Map Interpretation

• High pressure: clear, cool weather (north-clockwise, south-counterclockwise)

• Low pressure: cloudy, rainy weather, especially along fronts (cold or warm) (north-counterclockwise, south-clockwise)

• Cold fronts: Associated with a sharp drop in temperature and often precipitation

• Warm fronts: Associated with gradual temperature increases and light precipitation

• Occluded fronts: Occur when a cold front overtakes a warm front, often leading to complex weather patterns.

• Katabatic Winds: cold dense air pools over ice fields = high pressure; warm air over ocean = low pressure; air flows from high to low pressure down slopes; gravity

• Air moves from high to low pressure.

• Large pressure gradient = strong wind.

• Small gradient = weak wind.

• Wind speed/direction affected by Coriolis force and friction.

• In the Northern Hemisphere, winds bend $45°$ to the right of the steepest slope of the pressure gradient; in the Southern Hemisphere, they bend to the left.

Convective Loops and Breezes

• Convective loop: warm air rises (low pressure) and cooler air moves in to replace it (high pressure)
• Land breeze: At night, land cools faster than water, causing high pressure over the land and low pressure over the sea, causing air to move from land to sea.
• Sea breeze: During the day, land heats up faster than the sea, causing low pressure over the land and high pressure over the sea, causing air to move from sea to land.

Coriolis Effect and Geostrophic Wind

• Coriolis effect bends winds to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
  • The magnitude of Coriolis effect depends on: latitude and wind speed
  • Example: the dust storm winds are deflected to the right due to the Coriolis effect, even though the pressure gradient is from northeast to southwest in Sahara.
  • Coriolis and friction effects cause this change in direction.
• Coriolis force causes wind deflection (objects moving over the rotating Earth are deflected counter-clockwise relative to the geographic grid) making wind flow parallel to isobars (geostrophic wind) in high altitudes, where the pressure gradient force and Coriolis effect balance out
• Friction slows down winds near the Earth's surface, modifying their speed and direction

Cyclones and Anticyclones

• Cyclones: Low pressure systems where air converges and spirals inward counterclockwise in the Northern Hemisphere, clockwise in the Southern Hemisphere)
• Anticyclones: High pressure systems where air diverges and spirals outward (clockwise in the Northern Hemisphere, counterclockwise in the Southern Hemisphere)
• Wind flows: inward & upward in cyclones, outward & downward in anticyclones

Global Pressure Systems

• Intertropical Convergence Zone (ITCZ): Low pressure area near the equator, where the trade winds from the Northern and Southern Hemispheres meet.
• Doldrums: Calm areas near the ITCZ, with little horizontal wind motion.
• Subtropical highs: High pressure areas, cooled air sinks around $30°$ latitude, associated with deserts
• Trade winds: Winds that blow from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisphere, toward the ITCZ, predictable
• Subpolar low: Low pressure area around $60°$ latitude. Warmer air of the mid-latitudes rises as it meets cold polar air
• Polar high: High pressure areas near the poles. Cold and dense
• Low pressure at the equator (ITCZ), warm air rises, trade winds blow toward equator
• High pressure at $30°$ N/S (subtropical highs), descending dry air, westerlies blow poleward
• Low pressure at $60°$ N/S (subpolar lows), rising air, polar front zone
• High pressure at the poles, cold dense air sinks, polar easterlies blow outward
• Seasonal shift = pressure & wind belts move north in summer, south in winter due to solar heating differences

Climate and Location

• ITCZ: Tropical rainforests due to constant warm temperatures and high precipitation
• Subtropical highs: Deserts due to dry, sinking air.

Indian Monsoon

• Caused by the seasonal shift in wind direction: during the summer, the ITCZ moves northward, causing low pressure over India, leading to moisture-laden winds from the ocean and heavy rainfall (monsoon season).
• January: high pressure over the land produces dry winds, air flows towards the ITCZ
• July: position of the ITCZ moves North, low pressure over the land causes winds to flow off the ocean, this brings heavy rainfall.

Continental vs. Maritime Climates

• Continental locations (e.g., Khartoum, Sudan) tend to be drier because they are far from moisture sources like oceans.
• Maritime locations (e.g., Jaluit in the Marshall Islands) are wetter due to proximity to oceans and the moisture they bring.

Weather, Humidity, and the Adiabatic Lapse Rate

• Water exists in solid (ice), liquid (water), and gas (vapor) states
• Melting: energy added (latent heat of fusion)
• Evaporation (absorbs heat), condensation (releases heat), freezing (releases heat), melting (absorbs heat), sublimation (absorbs heat), deposition (releases heat)
• Evaporation and Evapotranspiration, precipitation, Interception (if trees are present), Overland Flow and Runoff, Surface Water, Infiltration, Aquifer Recharge, Groundwater Flow, Oceans
  • Evaporation occurs over open bodies of water
  • Evapotranspiration occurs when plants respire water into the atmosphere
  • Evapotranspiration can occur at a maximum rate called Potential Evapotranspiration when there is sufficient water available for the plants to respire
  • When there is insufficient soil moisture available, plants respire at a reduced rate called Actual Evapotranspiration This rate is approximately determined by the amount of moisture available
  • Interception: water caught by leaves/branches, then evaporates or is transpired
  • Infiltration: water sinks into soil up to infiltration capacity
  • Infiltration Capacity: higher in sandy & vegetated soils, lower in clay & bare soil
  • Urban areas = low infiltration → more overland flow
  • Overland flow: runs downslope, may enter soil or stream as runoff

Humidity

• Humidity is the amount of water vapour in the atmosphere

• Warm air can hold much more than cold air

  • Cold dry air can have close to $0\%$
  • Warm tropical air may have $4-5\%$

• Two ways to describe humidity (specific humidity and relative humidity)

• Specific Humidity is the actual quantity of water vapour in the air

  • Expressed as grams of water per kilogram of air $(g/kg)$
  • Used to describe the water content of large air masses, and how it varies by latitude
    • At $20ºC$, air can hold around 15 grams of water per kg of air
    • At $30ºC$, it is nearly double (26 g/kg)
  • Geographic Distribution: Higher in tropical areas, lower in polar regions

• Relative Humidity

  • percentage of moisture in the air compared to the maximum it can hold at a given temperature
  • Changes with temperature: If temperature increases while moisture stays constant, relative humidity decreases
  • Compares amount of water vapour present to the maximum amount that the air can hold at that temperature $(\%)$
    • E.g. if relative humidity is $50\%$, then it contains $1/2$ the amount it could given the temperature.
  • It therefore changes if temperature changes Relative Humidity and Temperature e.g. if temperature increases, if the amount of water vapor stays the same, then relative humidity decreases

• Dew point temperature

  • The temperature at which air reaches $100\%$ relative humidity and condensation begins
  • Temperature at which condensation begins under constant pressure and water vapour content
  • If air is cooled eventually it will be said to be saturated (100% relative humidity) = (dew point temperature)
  • If cooling continues, condensation begins and dew forms
  • If temperature drops, relative humidity increases if moisture remains the same

• Graph interpretation: Be able to determine changes in relative/specific humidity based on temperature variations

Adiabatic Lapse Rates and Cloud Formation

• Temperature steadily rises from morning to afternoon, peaking at midday, and then decreasing in the evening. Relative humidity, on the other hand, would show the opposite pattern—highest in the morning, decreasing as the temperature rises, and then increasing again as the temperature drops in the evening.
• Adiabatic means no heat exchange with the surroundings when air rises, it expands and cools (due to lower pressure) when air descends, it compresses and warms adiabatic lapse rate varies depending on the moisture content in the air
• Dry Adiabatic Lapse Rate (DALR): Unsaturated air cools at $10°C/km$ when rising and warms at $10°C/km$ when sinking
• Wet Adiabatic Lapse Rate (WALR): Saturated air cools at ~$5-9°C/km$ due to latent heat release at the dew point/lifting condensation level
• Associated with convectional precipitation
• As a parcel of air rises, it cools and becomes saturated at the dew point
• When it reaches its dew point, condensation occurs (lifting condensation level)
• Clouds form when rising air cools to its dew point, causing condensation
• Made up of water droplets and/or ice particles
• Form when air is saturated AND contains particles (condensation nuclei) e.g. dust, sea-salts.

Cloud Types and Fog

• Water can remain in liquid state below freezing (supercooled) to as low as $-12ºC$
• High Clouds: Cirrus, cirrostratus, cirrocumulus
• Middle Clouds: Altostratus, altocumulus
• Low Clouds: Stratus, stratocumulus, nimbostratus
• Cumuliform Clouds: Cumulus (fair weather), cumulonimbus (thunderstorms)
• Thunder cloud (cumulonimbus) extends from low to high
• Fog: cloud layer near the surface, forming in calm, clear weather
• Radiation fog: forms at night when ground air cools below dew point
• Advection fog: occurs when warm, moist air moves over a cool surface
• Sea fog: type of advection fog formed by cool marine air over cold ocean currents
• Fog formation: when warm, moist air cools below dew point near the surface
• Dew: forms when the ground cools faster than the air, while fog requires both to cool below dew point

Precipitation

• Clouds consist of tiny droplets of water that are constantly condensing and evaporating

• Condensation nuclei: tiny particles of dust, salt, etc., around which water condenses

• Growth of droplets: it takes time and the right conditions to form a full raindrop from droplets

• Ice-crystal process: ice particles act as freezing nuclei, making precipitation form faster, often starting as frozen water

• Coalescence process: larger droplets collide with smaller ones to form bigger droplets

• Rain: Liquid water droplets that fall when temperatures are above freezing.

• Snow: Ice crystals that fall when temperatures are below freezing.

• Sleet: Small ice pellets that form when rain freezes before hitting the ground. precipitation re-freezes before hitting the ground

• Hail: Larger ice pellets that form in strong thunderstorms.

• Freezing Rain

  • When precipitation falls through a warm atmospheric layer (temperature inversion), at least partially melts, and then falls through a sub-freezing atmospheric layer near the surface when the precipitation drops to the freezing point, but does not actually freeze until hitting a surface that is below freezing

Types of Precipitation

• Orographic: Air rising over mountains (e.g., U.S. West Coast)
  • Intercepting slope = Windward slope (wetter)
  • Leeward slope (drier) (rainshadow)
• Convectional: Warm air rises, cools to dew point, clouds form, latent heat release, adds energy and increases updraft, and condenses (associated with thunderstorms)
• Frontal: Air masses collide, forcing warm air up
• Unstable air, strong updrafts, cumulonimbus clouds, where air cools more rapidly than wet or dry adiabatic lapse rate, condensing air is warmer than surrounding air
• Convectional precipitation: occurs when warm, moist air rises due to heating from the surface, cooling as it moves upward, causing condensation and cloud formation

Thunderstorms and Related Phenomena

• Thunderstorms: form in unstable air when warm, moist air rises and cools, leading to the formation of cumulonimbus clouds; characterized by lightning, thunder, heavy rain, and sometimes hail
• Clouds: cumulonimbus clouds are typical, reaching great heights and capable of producing intense weather events
• Air movement: warm air rises, cooling and condensing into clouds, while cooler air sinks, creating strong updrafts and downdrafts that contribute to storm intensity
• Hail: Updrafts and downdrafts circulate hail stones, accumulate layers of ice on ice pellets
  • Lightning: Charge buildup in clouds discharges, heating air to ~$30,000°C$, causing thunder
  • Updrafts and downdrafts create positive and negative charges Only $20\%$ of strikes are from cloud to ground

Air Masses and Fronts

• Low pressure = stormy, High pressure = clear
• c = continental (dry) m = maritime (wet) T= tropical (warm) P = polar (cold) A = Arctic (cold) (from Arctic oceans and fringing lands air masses: large bodies of air with uniform temperature, humidity, and pressure
• Warm air: less dense, rises, moves faster
• Cold air: denser, sinks, moves slower
• Types of air masses
  • Tropical: warm, forms near the equator
  • Maritime: moist, forms over oceans
• cP (continental polar - dry, cold), mT (maritime tropical - warm, wet)
  • Tropical air masses are warm and moist, coming from near the equator.
  • Maritime air masses are moist and can be warm or cold, coming from over oceans.
  • Cold air is denser, moves faster, and generally brings clearer skies, while warm air is lighter, slower, and can lead to cloud formation and precipitation.
• Frontal systems: boundaries between air masses
• Cold front: cold air mass lifts a warm air mass aloft. The upward motion sets off a line of thunderstorms, cold air pushes into warm air, causes sudden temperature drops and storms
• Warm front: warm air advances toward cold air and rises up and over the cold air. Rain falls from the dense stratus cloud layer
• Stationary front: warm and cold air masses stall, causing prolonged cloudiness and light precipitation
  • Occluded front: cold front overtakes warm front, leading to mixed precipitation and stormy conditions
    *Mid-to-high latitudes: frontal interactions between warm tropical air and cold polar air create low-pressure systems and storms

Fronts and Wave Cyclones

• Cold Front: Cold air pushes into warm air, causes rapid lifting and intense storms (thunderstorms, hail), moves quickly.
  • Move quickly, typically 20-30 mph.
• Warm Front: Warm air slides over cold air, causes light to moderate precipitation (rain, drizzle), moves slowly.
  • Move slower, around 10-15 mph.
• Occluded Front: Cold front catches warm front, lifts warm air, causes complex weather (rain, snow), moves slowly. Form when a fast-moving cold front catches up to a slower-moving warm front, lifting the warm air off the ground. This results in a complex weather system with mixed precipitation.
• Wave Cyclones: form in certain areas and travel common paths, Low-pressure systems that form along a front where warm and cold air masses meet. They are characterized by a wavelike shape on the front, which leads to the development of multiple types of fronts and associated weather patterns.

Frontal Systems in Wave Cyclones:

• Cold Front: The cold air mass moves quickly and pushes under the warm air mass, causing the warm air to rise, leading to thunderstorms or heavy precipitation.
• Warm Front: The warm air gradually slides over the cold air mass, bringing steady, prolonged precipitation as the warm air ascends and cools.
• Occluded Front: Occurs when the cold front catches up with the warm front, lifting the warm air off the ground, leading to a mix of precipitation (rain, snow, sleet) and often cloudy skies.

Weather Map Interpretation

• Weather maps show relationships between: systems that might commonly occur on the east coast (e.g. storm systems from the mid-west into CT or hurricanes in FL)

Tropical and Mid-Latitude Cyclones

• Tropical cyclones (hurricanes, typhoons, cyclones)

  • form over warm tropical oceans initially move westward due to easterly trade winds in the northern hemisphere, they curve northward due to the coriolis effect once they reach mid-latitudes, westerlies push them eastward common east coast impact: hurricanes that move up the coast, sometimes turning inland

• Mid-latitude cyclones

  • form along the polar front where cold and warm air masses meet travel west to east due to prevailing westerlie often bring storm systems from the midwest into new england common east coast impact: nor’easters, frontal storms, heavy rain, or snow

Satellite Images

• hurricanes appear as circular storms with a defined eye, while mid-latitude cyclones often have a comma-shaped cloud pattern.

The Intertropical Convergence Zone (ITCZ)

• Band of rising air near the equator.
• Important for global weather patterns and tropical rainfall

Seasonal Variability:

• Global wind and pressure patterns shift with the seasons Know the factors that form tornadoes and where they tend to occur.

Tornadoes & Tropical Cyclones

• Thunderstorms: Tornadoes usually form from severe thunderstorms, particularly those with a supercell structure.
• Wind shear: A significant change in wind speed or direction with height in the atmosphere creates rotation, which can develop into a tornado.
• Updrafts: Strong, rotating updrafts in thunderstorms help organize the wind shear and increase the potential for tornado formation.
• Instability: Warm, moist air at the surface and cool, dry air aloft can create atmospheric instability, making tornadoes more likely.

Tornado Stages of Development

• Stage 1 - Formation: Tornadoes begin as a rotating updraft called a mesocyclone in a thunderstorm. When a funnel cloud forms and reaches the ground, it becomes a tornado.
• Stage 2 - Mature Stage: The tornado is fully developed, often with a visible, condensed funnel and strong wind speeds that cause damage.
• Stage 3 - Decay Stage: The tornado weakens and eventually dissipates. The funnel may shrink and the rotation decreases.

Potential Impacts of Tornadoes

• Wind damage: Tornadoes can produce winds over 300 mph, causing extreme destruction to buildings, vehicles, and infrastructure.
• Debris: Flying debris is a major hazard, often responsible for injuries and fatalities.
• Flooding: Sometimes, tornadoes occur alongside thunderstorms that bring heavy rainfall, which can lead to flooding.

Cyclone Information

• Warm sea surface temperatures: ocean must be at least $80°F (27°C)$ to provide the heat and moisture necessary for the storm's development.
• Low vertical wind shear: Minimal changes in wind speed and direction with height allow the storm to remain organized.
• Moisture in the atmosphere: constant supply of warm, moist air is essential for sustaining a tropical cyclone.
• Pre-existing disturbance: disturbance, such as a tropical wave, provides the initial rotation and low-pressure area around which a cyclone can form Rainbands: Bands of showers and thunderstorms that spiral out from the center, bringing heavy rain and winds.
  • Rainbands: Bands of showers and thunderstorms that spiral out from the center, bringing heavy rain and winds.
• Hurricanes (western hemisphere) and typhoons (western Pacific in Asia) and cyclone in Indian Ocean
• Develop over warm ocean surfaces between $8°$ and $15°$ latitude, migrate westward and curve toward the poles

Tropical Cyclone Weakening Factors

• Cool sea surface temperatures: Lack of warm water reduces the energy supply to the storm.
• High wind shear: Strong winds at higher altitudes can disrupt the storm's structure.
• Land interaction: Tropical cyclones lose their strength when they move over land due to the loss of heat and moisture.
• Dry air: If dry air is pulled into the system, it can weaken the storm.

Damaging Effects of Tropical Cyclones

• Strong winds: High winds can cause widespread damage to buildings, trees, and power lines.
• Heavy rainfall: Can lead to flooding, particularly in coastal areas.
• Storm surges: A rise in sea level caused by the cyclone’s winds pushing water towards the shore, often causing coastal flooding.
• Tornadoes: Hurricanes and typhoons can spawn tornadoes as they move over land.

Saffir–Simpson Scale

• Category 1: Winds 74-95 mph (119-153 km/h) – Minimal damage.
• Category 2: Winds 96-110 mph (154-177 km/h) – Extensive damage.
• Category 3: Winds 111-129 mph (178-208 km/h) – Devastating damage.
• Category 4: Winds 130-156 mph (209-251 km/h) – Catastrophic damage.
• Category 5: Winds 157 mph or higher (252 km/h or higher) – Catastrophic damage with widespread destruction.

Hydrology

The Hydrologic Cycle

• The hydrologic cycle describes the continuous movement of water on, above, and below the surface of the Earth. It includes processes such as evaporation, transpiration, condensation, precipitation, infiltration, runoff, and groundwater flow.
• The water balance is the relationship between precipitation, evapotranspiration, and water storage in an area over time.
• Oceans: $97.2\%$ of Earth's water
• Glaciers and Ice Caps: $2.15\%$
• Groundwater: $0.62\%$
• Surface Water (Lakes, Rivers, Wetlands): $0.02\%$
• Atmospheric Water Vapor: $0.001\%$
• Evaporation & Evapotranspiration: Water moves from surfaces (lakes, oceans) and plants (transpiration) into the atmosphere.
• Precipitation: Water falls as rain, snow, sleet, or hail.
• Interception: Some precipitation is caught by vegetation.
• Infiltration: Water sinks into the ground.
• Overland Flow & Runoff: Excess water flows across the surface into rivers and lakes.
• Groundwater Flow & Aquifer Recharge: Water percolates underground and replenishes aquifers.
• Oceans: Final destination for most water flow

Evapotranspiration

• Potential Evapotranspiration (PET): Maximum rate at which plants can transpire when water is available.
• Actual Evapotranspiration (AET): actual rate at which plants transpire, dependent on soil moisture

Precipitation Types

• Rain: Liquid water falling from clouds.
• Snow: Ice crystals that form in cold clouds.
• Sleet: Ice pellets formed when rain passes through freezing air.
• Freezing Rain: Supercooled liquid rain that freezes upon contact with surfaces.
• Evaporation – process where water changes from liquid to vapor due to heat from the sun. it occurs over oceans, lakes, rivers, and soil.
  • Higher evaporation rates occur in warm, dry, and windy conditions.
  • Lower evaporation rates occur in cool, humid, and calm conditions.
• Precipitation – water falling from the atmosphere as rain, snow, sleet, or hail. it replenishes groundwater, rivers, and lakes.
  • High precipitation areas – near the equator (e.g., tropical rainforests) and mid-latitudes with frequent storms.
  • Low precipitation areas – deserts and arid regions where evaporation exceeds precipitation.

Soil water changes

• balance between evaporation & precipitation regions where precipitation > evaporation (humid areas) have surplus water, leading to rivers, lakes, and wetlands. regions where evaporation > precipitation (arid areas) often face water shortages and rely on groundwater. climate change can intensify these processes, causing extreme droughts in some areas and increased flooding in others
• Soil Moisture Recharge: Occurs when precipitation exceeds evapotranspiration, refilling soil moisture.
• Soil Moisture Deficit: Occurs when evapotranspiration exceeds precipitation, leading to dry conditions.
• Soil Moisture Drawdown: use of stored water by plants.
• Soil Moisture Excess: When soil is fully saturated, leading to runoff.
• Interception: Vegetation captures precipitation, reducing runoff
• Infiltration: Water soaks into the ground, depending on soil type (higher in sand, lower in clay).
• Overland Flow: Excess water flows over the land when infiltration capacity is exceeded.

Human Impact

• Urbanization, deforestation, and agriculture reduce infiltration and increase runoff, leading to erosion and flooding.

Infiltration Capacity

• Maximum rate at which soil can absorb water

  • High in sandy soils, low in clayey soils. Higher in vegetated areas than bare soil Exceeded capacity leads to overland flow and runoff

Surface Water

• Discharge: volume of water moving through a river channel (Discharge = velocity x cross-sectional area).
• Hydrographs: Graphs showing river discharge over time. Sharp peaks indicate rapid runoff; gradual peaks suggest sustained baseflow.

River System Components

• Trunk – main river channel into which tributaries flow. it carries the majority of the water and sediment.
• Tributaries – smaller streams that feed into the trunk river, increasing its flow.
• Drainage basin (catchment area) – the land area that collects precipitation and directs it into streams and rivers. all water within a drainage basin eventually flows into a single river system.
• Drainage divide – boundary separating different drainage basins. rain falling on one side of a divide flows into one basin, while rain on the other side flows into a different basin.
• Drainage network – pattern of interconnected streams and rivers within a basin. it varies based on topography, rock type, and climate.

Discharge

Discharge (the volume of water flowing through a river per unit time) depends on the size of the drainage basin and the climate:

• Small basins – react quickly to storms, producing sharp, high peaks in discharge (peaky hydrographs). little baseflow.
• Moderate basins (e.g., fenton river) – have some groundwater-fed baseflow but still respond strongly to storms, showing peaky discharge patterns.
• Large basins (e.g., mississippi river) – dominated by baseflow and seasonal changes (e.g., snowmelt). storm impacts are less visible as they are mixed with inputs from multiple tributaries.

Floods

• Occur when water exceeds the capacity of a river, lake, or drainage system, often due to heavy rainfall, snowmelt, or storm surges
• Flood timing: varies based on climate, season, and geography—spring floods often come from snowmelt, while flash floods occur after intense storms
• 100-year flood: flood with a $1\%$ chance of occurring in any given year, not one that happens exactly every 100 years food graphs: show river discharge over time, helping predict peak flood times and understand flood risks based on past events

Concepts

• Stream velocity: the speed at which water moves through a stream, affected by channel shape, slope, and friction
• Stream discharge: the total volume of water flowing past a point in a stream per unit of time, calculated as discharge = velocity × cross-sectional area
• Causes: Heavy rainfall, snowmelt, low infiltration, and urbanization.
• 100-Year Flood: A flood with a 1% chance of occurring in any given year.
• Baseflow: Groundwater-fed, steady year-round.

Stages of water flow & discharge

• Base flow – normal, low-level discharge fed by groundwater. occurs during dry periods.
• Rising stage – discharge increases as runoff from rain or snowmelt enters the river.
• Peak flow (flood stage) – maximum discharge, often causing flooding if water exceeds channel capacity.
• Falling stage (recession) – discharge decreases as runoff slows and water drains downstream.
• Return to base flow – water levels stabilize, returning to groundwater-fed flow.

Water Supply

• Freshwater makes up only about $2.5\%$ of earth’s total water supply. most of it is stored in inaccessible places:
  • Glaciers & ice caps ($69\%$
  • Groundwater ($30\%$
  • Surface water (Oceans
  • Groudwater

Ground water

• Percolation & Aquifers: Water infiltrates through soil into underground reservoirs.
• Unconfined Aquifer: Directly connected to the surface, recharged by infiltration.
• Confined Aquifer: Trapped between impermeable layers, under pressure.
  Acquitard: Impermeable layer preventing water movement

Wells and Springs

• Well: Requires pumping.
• Artesian Well: Flows naturally under pressure.
• Flowing Artesian Well: Water flows without pumping.

Other

• Cone of Depression: Lowering of the water table from excessive pumping Pollution & Groundwater Flow: Contaminants follow the hydrologic gradient toward streams and wells
• In arid regions, water is scarce, yet demand is high due to agriculture, urban growth, and industry. groundwater is often the main source of water, but excessive withdrawal leads to aquifer depletion, causing long-term problems.

Examples of aquifer use

• Ogallala aquifer (great plains): supplies water to eight states, mainly for irrigation. declining water levels threaten farming and rural economies.
• Central valley aquifer (california): over-pumped for agriculture, leading to land subsidence (sinking ground) and reduced water availability. Pros
• Colorado river basin: serves arid states like arizona, nevada, and california, but heavy use has drained reservoirs, leading to water shortages.
• Floridan aquifer (southeast us): overuse and saltwater intrusion impact drinking water supplies.

Pros

• Provides a reliable water source

• Supports area agriculture

• Allows urban expansion is areas w/scares water

• Can be cleaner than surface water due to filtration. -Cons-Overuse lowers water tables, causing wells to dry.Subsidence damages buildingSalt water intrusion can contaminate groundwater.

• Solutions to groundwater depletion

• Water conservation: using drip irrigation, drought-resistant crops, and efficient household water use managed aquifer recharge: directing excess rainwater or treated wastewater back into aquifers

  Weather Resource Problems

• Water conservation: using drip irrigation, drought-resistant crops, and efficient household water use managed aquifer recharge: directing excess rainwater or treated wastewater back into aquifers:

• Desalination: Converting seawater into freshwater (costly but viable in coastal areas) Better policies: Regulating groundwater use to prevent over-extraction reuse & recycling: Using treated wastewater for irrigation and industrial purposes

Flood Management

• Channelization: Straightening rivers to speed flow (increases erosion and flood risk downstream Levees: Protect floodplains but can fail Wetland Restoration: Absorbs floodwaters naturally.
• Better to allow natural flooding
• Wetlands act as natural sponges

Household Water Use Impact

• Urbanization Impacts: Reduces infiltration, increases runoff, worsens floods. Household Water Conservation: Fix leaks, use efficient appliances. Reduce lawn irrigation, use native plants. Use rainwater collection and low-flow fixtures Agricultural Water Conservation: Drip irrigation, mulching, reducing over-irrigation Module 9: Landforms Fluvial Processes and Landforms Fluvial processes refer to the actions of running water in shaping the Earth's surface. These processes include erosion, transportation, and deposition, which together form landforms such as valleys, floodplains, deltas, meanders, oxbow lakes, and alluvial fans.

Fluvial Processes

• Erosion: The breakdown and removal of rock and soil by water Denudation: The overall wearing away of the Earth's surface by erosion and weathering. Transport: The movement of sediment by waterDeposition: The accumulation of transported material in new locations
• Sheet Erosion: The removal of thin layers of soil by water Rills: Small channels formed by running water on slopes Gullies: Larger, more defined channels formed by prolonged erosion Channel Erosion: The deepening and widening of stream channels Vegetation: Helps to stabilize soil, reducing erosion rates Balance of Soil: Normally, the amount of soil lost through erosion is balanced by new soil formation from weathering
• Unsorted sediment that accumulates at the